The apparatus has, in particular, a piezoelectric transformer, which generates an output voltage that can be used for ionization of a process gas. The apparatus is intended to prevent movements of the piezoelectric transformer, in particular in a longitudinal direction, relative to a mount of the apparatus. However, at the same time, the mount is intended not to interfere with the piezoelectric transformer in such a way that oscillations of the transformer are damped, since this would reduce the efficiency of the plasma generation.